Extreme ultraviolet lithography mask and multilayer deposition method for fabricating same

ABSTRACT

A mask, method of fabricating same, and method of using same are disclosed. In an example, a mask includes a substrate and a reflective multilayer coating deposited over the substrate. The reflective multilayer coating is formed by positioning the substrate such that an angle α is formed between a normal line of the substrate and particles landing on the substrate and rotating the substrate about an axis that is parallel with a landing direction of the particles. In an example, reflective multilayer coating includes a first layer and a second layer deposited over the first layer. A phase defect region of the reflective multilayer coating includes a first deformation in the first layer at a first location, and a second deformation in the second layer at a second location, the second location laterally displaced from the first location.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. In the course of IC evolution,functional density (i.e., the number of interconnected devices per chiparea) has generally increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased. This scaling down process generally provides benefits byincreasing production efficiency and lowering associated costs. Suchscaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are needed. For example,higher resolution lithography processes, such as extreme ultraviolet(EUV) lithography processes, are implemented to meet size constraintsapproaching critical dimension tolerances of 32 nm technology nodes andbelow. EUV lithography uses a reflective mask (also referred to as areticle) to transfer a pattern of a layer of an integrated circuitdevice to a wafer. A reflective mask typically includes a reflectivemultilayer coating (multilayer mirror) deposited on a substrate. Anydefects, including microscopic defects, in the substrate causesdeformations in material layers of the reflective multilayer coatingthat undesirably affect printability of the pattern of the reflectivemask. Such defects are often difficult to inspect and, even if detected,difficult to repair. Accordingly, although existing EUV masks andmethods of manufacturing EUV masks have been generally adequate fortheir intended purposes, they have not been entirely satisfactory in allrespects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a diagrammatic cross-sectional side view of a mask accordingto various aspects of the present disclosure.

FIG. 2 is a flow chart of a method for forming a material layer of amask according to various aspects of the preset disclosure.

FIG. 3 is a schematic view of forming a material layer of a mask usingthe method of FIG. 2 according to various aspects of the presentdisclosure.

FIG. 4 is a diagrammatic cross-sectional side view of a mask fabricatedusing the method of FIG. 2 according to various aspects of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed. Further, spatiallyrelative terms, such as “beneath,” “below,” “lower,” “above,” “upper”and the like, may be used herein for ease of description to describe oneelement or feature's relationship to another element(s) or feature(s) asillustrated in the figures. The spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thedevice in the figures is turned over, elements described as being“below” or “beneath” other elements or features would then be oriented“above” the other elements or features. Thus, the exemplary term “below”can encompass both an orientation of above and below. The apparatus maybe otherwise oriented (rotated 90 degrees or at other orientations) andthe spatially relative descriptors used herein may likewise beinterpreted accordingly.

FIG. 1 is a diagrammatic cross-sectional side view of a mask 100 (alsoreferred to as a photomask or a reticle) according to various aspects ofthe present disclosure. In the depicted embodiment, the mask 100 is amask blank that will undergo a mask fabrication process to pattern themask blank with a design of a layer of an integrated circuit (IC)device. FIG. 1 has been simplified for the sake of clarity to betterunderstand the inventive concepts of the present disclosure. Additionalfeatures can be added in the mask 100, and some of the featuresdescribed below can be replaced or eliminated for additional embodimentsof the mask 100.

The mask 100 includes a substrate 110. The substrate 110 has a surface112 and a surface 114 that is opposite the surface 112. In the presentexample, the substrate 110 includes a low thermal expansion material(LTEM). In an example, the LTEM substrate includes titania (TiO₂) dopedfused silica (SiO₂). Alternatively, the substrate 110 includes othermaterials, such as quartz or glass, depending on design requirements ofthe mask 100.

A reflective multilayer coating (RMLC) 120 (also referred to as amultilayer mirror (MLM)) is deposited over the substrate 110,particularly over a surface 112 of the substrate 110. The RMLC 120includes multiple material layers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122_(N), where N is a total number of the material layers of the RMLC 120.Hereafter, for ease of discussion, “a material layer” or “materiallayers” is simply referred to as “a layer” or “layers.” In the presentexample, in relation to the surface 112 of the substrate 110, the layer122 ₁ may be referred to as a bottommost layer of the RMLC 120, and thelayer 122 _(N) may be referred to as the topmost layer of the RMLC 120.In furtherance of the present example, the multiple layers 122 ₁, 122 ₂,122 ₃, 122 ₄, . . . , 122 _(N) form a number of layer pairs, where eachlayer pair includes two layers having different refractive indices (inother words, a combination of a first material and a second material,where a refractive index of the first material is different than arefractive index of the second material). For example, a layer pairincludes layer 122 ₁ and layer 122 ₂, another layer pair includes layer122 ₃ and layer 122 ₄, and so forth. The combination of the materials inthe layer pair is selected to provide a large difference in refractiveindices between the two layers (for example, to achieve largereflectivity at an interface of the two layers according to Fresnelequations), yet to provide small extinction coefficients for the layers(for example, to minimize absorption). In an example, the RMLC 120includes molybdenum-silicon (Mo/Si) layer pairs. In another example, theRMLC 120 includes molybdenum-beryllium (Mo/Be) layer pairs. A thicknessof each layer of each layer pair of the RMLC 120 is adjusted dependingon a wavelength and an angle of incidence of light (such as extremeultraviolet (EUV) radiation) incident on the mask 100, such that themask 100 achieves maximum constructive interference of light reflectedfrom different interfaces of the RMLC 120. In general, reflectivity ofthe RMLC increases as a number of layer pairs of the RMLC 120 increases.Accordingly, in principle, if the number of layer pairs is sufficientlylarge and extinction coefficients of the materials of the layers in thelayer pairs are close to zero, reflectivity of the RMLC 120 can approach100% regardless of the difference of the refractive indices of thematerials of the layers in the layer pairs. However, in the EUVwavelength range, the highest reflectivity that can be achieved islimited by the extinction coefficients of the materials employed for thelayers of the RMLC 120. In the present example, the number of layerpairs of the RMLC 120 is about twenty pairs to about eighty pairs. Forexample, in the depicted embodiment, to achieve more than 95%reflectivity of the RMLC 120 and minimize mask blank manufacturing timeand costs, the RMLC 120 includes about forty layer pairs, such as fortyMo/Si pairs (where N=80; layers 122 ₁, 122 ₃, . . . , 122 ₇₉ includesilicon and have a thickness of about 2 nm to about 6 nm (for example,about 4 nm); and layers 122 ₂, 122 ₄, . . . , 122 ₈₀ include molybdenumand have a thickness of about 1 nm to about 5 nm (for example, 3 nm).Alternatively, the RMLC 120 includes any other number of layer pairs,depending on reflectivity specifications for the mask 100. In otheralternatives, the RMLC 120 may include layer groups, in other words,groups of three or more layers having different refractive indices andother characteristics to maximize reflectivity.

The RMLC 120 includes a phase defect region that alters a phase of lightreflected from the RMLC 120. In the depicted embodiment, a defect 130,such as a bump defect, is located at the surface 112 of the substrate110. As illustrated in FIG. 1, the defect 130 causes a deformation inthe layers of the RMLC 120 deposited on the surface 112 of the substrate110. More specifically, a deformation occurs in each of the layers 122₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N) of the RMLC 120. The defect 130thus propagates into each successively formed layer, such that the phasedefect region of the RMLC 120 extends from the bottommost layer (layer122 ₁) to the topmost layer (layer 122 _(N)). Alternatively, the phasedefect region extends through a limited number of the layers 122 ₁, 122₂, 122 ₃, 122 ₄, . . . 122 _(N) of the RMLC 120. In yet anotheralternative, where the phase defect region extends through a limitednumber of the layers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N), adefect in/on one of the layers causes deformations in the subsequentlydeposited layers, such that the deformations in the subsequentlydeposited layers are associated with the defect in/on the layer, insteadof a defect in the substrate 110, such as the defect 130. Each of thedeformations of the layers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N)associated with the defect 130 is located at a substantially samelateral location, in the present example, a substantially samex-coordinate. For example, each deformation has a profile having a fullwidth at half maximum (FWHM), and in the depicted embodiment, a laterallocation of a center of each deformation's FWHM has a substantially samex-coordinate, while a vertical location of the center of eachdeformation's FWHM is at a different y-coordinate. The location of thecenter of each deformation's FWHM is thus at substantially the samelateral location for layers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N).The x- and y-coordinates are merely used for example, and thus are notintended to be limiting. Further, the profile of the deformations inlayers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N) illustrated in FIG. 1are merely examples, and the deformations of the RMLC 120 may have adifferent profile depending on the type of defect associated with thedeformations and the processing conditions during the forming of thelayers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N) of the RMLC 120.

Light reflected from the RMLC 120 consists of the light reflected fromthe different interfaces of the RMLC 120. In the present example, lightreflected from the different interfaces in the phase defect region arephase shifted (in other words, have phase errors) because of thedeformations of the layers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N) inthe RMLC 120 (here, resulting from the defect 130). The illustratedphase defect region (the collection of deformations in the layers of theRMLC 120) thus largely impacts a phase of the light reflected from theRMLC 120, though it may minimally impact an amplitude of such reflectedlight. When small imaging wavelengths, such as EUV wavelengths, are usedwith the mask 100, the phase errors introduced in the reflected light bythe phase defect region of the RMLC 120 can be large, even if thedeformations in the layers 122 ₁, 122 ₂, 122 ₃, 122 ₄, . . . 122 _(N)associated with the phase defect region of the RMLC 120 may be small.For example, when the imaging wavelength is 13.5 nm, a defect having aheight or depth of about 3.4 nm (about one fourth of the imagingwavelength) can introduce a phase error as much as 180°. Such phaseshifts (errors) resulting from the phase defect region of the RMLC 120thus negatively impact the lithography processes using the mask 100. Infact, a phase error smaller than 180°, for example, as small as 20°, cannegatively impact a lithography process window or patterning fidelityusing the mask 100. Accordingly, it is desired that the substrate 110(particularly the surface 112 of the substrate 110), as well as the RMLC120, is free of defects, such as bump defects, pit defects, and othertypes of defects. However, achieving a defect free substrate, as well asa defect free RMLC, is difficult using conventional technology. Thefollowing discussion thus examines how to reduce the impact of suchdefects, particularly, the impact of phase defect regions that resultfrom such defects.

FIG. 2 is a flow chart of a method 200 for forming a layer of a mask,and FIG. 3 is a schematic view of forming a layer of a mask using themethod 200 of FIG. 2, according to various aspects of the presentdisclosure. In the present example, the method 200 forms a reflectivemultilayer coating (RMLC) of a mask 300. Alternatively, the method 200may be used to form other layers of the mask 300. FIG. 4 is adiagrammatic cross-sectional side view of a mask, such as the mask 300,fabricated using the method of FIG. 2, according to various aspects ofthe present disclosure. FIGS. 2-4 will be discussed concurrently andhave been simplified for the sake of clarity to better understand theinventive concepts of the present disclosure. Additional steps can beprovided before, during, and after the method 200, and some of the stepsdescribed can be replaced or eliminated for additional embodiments ofthe method 200. Additional features can be added in the mask 300, andsome of the features described below can be replaced or eliminated foradditional embodiments of the mask 300.

Referring to FIGS. 2-4, at block 210, a substrate 310 of the mask 300 isprovided. The substrate 310 has a surface 312 and a surface 314 that isopposite the surface 312. In the present example, the substrate 310includes a low thermal expansion material (LTEM), such as titania (TiO₂)doped fused silica (SiO₂). Alternatively, the substrate 310 includesother materials depending on design requirements of the mask 300. Thesubstrate 310 includes a defect 330 located at the surface 312. In thepresent example, the defect 330 is a bump defect. The defect 330 mayalternatively be a pit defect or other type of surface defect.

At block 220, a reflective multilayer coating (RMLC) 320 (also referredto as a multilayer mirror (MLM)) is formed over the substrate 310,particularly over the surface 312 of the substrate 310. The RMLC 320includes multiple layers 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . 322 _(N),where N is a total number of the layers of the RMLC 320. Hereafter, forease of discussion, “a material layer” or “material layers” is simplyreferred to as “a layer” or “layers.” In the present example, inrelation to the surface 312 of the substrate 310, the layer 322 ₁ may bereferred to as a bottommost layer of the RMLC 320, and the layer 322_(N) may be referred to as a topmost layer of the RMLC 320. Infurtherance of the present example, the multiple layers 322 ₁, 322 ₂,322 ₃, 322 ₄, . . . , 322 _(N) form a number of layer pairs, where eachlayer pair includes two layers having different refractive indices (inother words, a combination of a first material and a second material,where a refractive index of the first material is different than arefractive index of the second material). For example, a layer pairincludes layer 322 ₁ and layer 322 ₂, another layer pair includes layer322 ₃ and layer 322 ₄, and so forth. The combination of the materials inthe layer pair is selected to provide a large difference in refractiveindices between the two layers (for example, to achieve largereflectivity at an interface of the two layers according to Fresnelequations), yet provide small extinction coefficients for the layers(for example, to minimize absorption). In an example, the RMLC 320includes molybdenum-silicon (Mo/Si) layer pairs. In another example, theRMLC 320 includes molybdenum-beryllium (Mo/Be) layer pairs. A thicknessof each layer of each layer pair of the RMLC 320 is adjusted dependingon a wavelength and an angle of incidence of light (such as extremeultraviolet (EUV) radiation) incident on the mask 300, such that themask 300 achieves maximum constructive interference of light reflectedfrom different interfaces of the RMLC 320. In general, reflectivity ofthe RMLC increases as a number of layer pairs of the RMLC 320 increases.Accordingly, in principle, if the number of layer pairs is sufficientlylarge and extinction coefficients of the materials of the layers of thelayer pairs are close to zero, reflectivity of the RMLC 320 can approach100% regardless of the difference of the refractive indices of thematerials of the layers in the layer pairs. However, in the EUVwavelength range, the highest reflectivity that can be achieved islimited by the extinction coefficients of the materials employed for thelayers of the RMLC 320. In the present example, the number of layerpairs of the RMLC 320 is about twenty pairs to about eighty pairs. Forexample, in the depicted embodiment, to achieve more than 95%reflectivity of the RMLC 320 and minimize mask blank manufacturing timeand costs, the RMLC 320 includes about forty layer pairs, such as fortyMo/Si pairs (where N=80; layers 322 ₁, 322 ₃, . . . , 322 ₇₉ includesilicon and have a thickness of about 2 nm to about 6 nm (for example,about 4 nm); and layers 322 ₂, 322 ₄, . . . , 322 ₈₀ include molybdenumand have a thickness of about 1 nm to about 5 nm (for example, 3 nm).Alternatively, the RMLC 320 includes any other number of layer pairs,depending on reflectivity specifications for the mask 300. In otheralternatives, the RMLC 320 may include layer groups, in other words,groups of three or more layers having different refractive indices andother characteristics to maximize reflectivity.

During the forming of the RMLC 320, the substrate 310 is tilted androtated such that any deformation formed in the RMLC 320 is laterallydisplaced. In FIG. 3, lines 305 represent particles landing on thesubstrate 310 during the forming of the RMLC 320. The particles landingon the substrate 310 form the various layers 322 ₁, 322 ₂, 322 ₃, 322 ₄,. . . 322 _(N) of the RMLC 320. In an example, an ion beam sputteringprocess forms the RMLC 320, and the lines 305 represent sputteredparticles landing on the substrate 310. Alternatively, other depositionprocesses may be used to form the RMLC 320. In FIG. 3, a line (or axis)R, represents a line parallel with a landing direction of the particles(lines 305). The substrate 310 is tilted such that an angle α is formedbetween a normal line (N) of the substrate 310 and the landing directionof the particles (lines 305) landing on the substrate 310, and rotatedabout an axis that is parallel with the landing direction of theparticles (lines 305). The angle α is greater than 0°, for example, theangle α is greater than about 20° and less than about 70°. In thepresent example, the substrate 310 is rotated about the line (or axis)R, which is parallel with the landing direction of the particles (lines305). The substrate 310 may be rotated about other lines (or axes) thatare parallel with the landing direction of the particles.

By tilting the substrate 310 such that the angle α is formed between thenormal line (N) of the substrate 310 and a landing direction of theparticles (lines 305) and rotating the substrate 310 about the axis thatis parallel with the landing direction of the particles (lines 305), anydeformation formed in at least two layers of the RMLC 320 is laterallydisplaced. In FIG. 4, the RMLC 320 includes a laterally displaced phasedefect region, achieved by the tilting and rotating of the substrate 310as depicted in FIG. 3. In the depicted embodiment, the laterallydisplaced phase defect region of the RMLC 320 is associated with thedefect 330 located at the surface 312 of the substrate 310, such thatthe laterally displaced phase defect region extends from the bottommostlayer (layer 322 ₁) to the topmost layer (layer 322 _(N)), where each ofthe deposited layers 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . 322 _(N) includesa deformation associated with the defect 330. Alternatively, thelaterally displaced phase defect region extends through a limited numberof the layers 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . 322 _(N) of the RMLC320. In yet another alternative, where the laterally displaced phasedefect region extends through a limited number of the layers 322 ₁, 322₂, 322 ₃, 322 ₄, . . . 322 _(N), a defect in/on one of the layers causesdeformations in the subsequently deposited layers, such thatdeformations in the subsequently deposited material layers areassociated with the defect in/on the layer, instead of a defect in/onthe substrate 310, such as the defect 330.

By tilting and rotating the substrate 310 as depicted in FIG. 3 duringthe forming of the RMLC 320, a lateral position (location) of thedeformations in each of the layers 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . ,or 322 _(N) of the RMLC 320 is shifted by a displacement in a samedirection (in the present example, in the right direction as shown inFIG. 4) with respect to a lateral location of the deformation of thepreviously deposited layer 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . , or 322_(N). For example, a lateral location of the deformation in the layer322 ₂ is displaced a distance in the positive x-direction from a laterallocation of the deformation in the layer 322 ₁; a lateral location ofthe deformation in the layer 322 ₄ is displaced a distance in thepositive x-direction from a lateral location of the deformation in thelayer 322 ₃; and so on. Each of the deformations of the layers 322 ₁,322 ₂, 322 ₃, 322 ₄, . . . 322 _(N) associated with the defect 330 isthus located at a different lateral location, in the present example, adifferent x-coordinate position. In the depicted embodiment, eachdeformation has a profile having a full width at half maximum (FWHM),and a lateral location of a center of each deformation's FWHM has adifferent x-coordinate, and a vertical location of the center of eachdeformation's FWHM is at a different y-coordinate. As noted, the laterallocation shifts a distance in a same direction, the right direction, foreach subsequently deposited layer. More specifically, a lateral locationof the center of the FWHM of the deformation in the layer 322 ₂ isdisplaced laterally to the right a distance from a lateral location ofthe center of the FWHM of the deformation in the layer 322 ₁; a laterallocation of the center of the FWHM of the deformation in the layer 322 ₄is displaced laterally to the right a distance from a lateral locationof the center of the FWHM of the deformation in the layer 322 ₃; and soon. In an example, a lateral location of the center of the FWHM of thedeformation in the layer 322 _(N) is displaced laterally to the right adistance, d_(x), from a lateral location of the center of the FWHM ofthe deformation in the layer 322 ₁, and a vertical location of thecenter of the FWHM of the deformation in the layer 322 _(N) is displacedvertically a distance, d_(y), from a vertical location of the center ofthe FWHM of the deformation in the layer 322 ₁. In an example, lateraldisplacement between the deformation in the layer 322 ₁ and thedeformation in the layer 322 _(N) is about 0.5 times to about 2.5 timesthe vertical displacement between the deformations of the layers 322 ₁and 322 _(N) (in other words, 2.5 d_(y)≧d_(x)≧0.5 d_(y)). The x- andy-coordinates, and the shifting direction, are merely used for example,and thus are not intended to be limiting. Further, the profile of thedeformations in layers 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . 322 _(N)illustrated in FIG. 4 are merely examples, and the deformations of theRMLC 320 may have a different profile depending on the type of defectassociated with the deformations and the processing conditions duringthe forming of the layers 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . 322 _(N) ofthe RMLC 320. In the present example, a thickness of each layer in aleft side of the deformation is different than a thickness of the layerin a right side of the deformation. Referring to layer 322 ₁, athickness of the layer 322 ₁ in a left side of the deformation is lessthan a thickness of the layer 322 ₁ in a right side of the deformation.In an example, shifting of the lateral location of each deformation mayresult from such thickness variation, which can occur when an amount ofparticles landing on the left side of the defect 330 is different thanan amount of particles landing on the right side of the defect 330. Thethickness variation in the deformation's profiles of the RMLC 320illustrated in FIG. 4 is merely an example, as any deformation profileis contemplated by the present disclosure so long as a lateral locationof a deformation associated with the phase defect region in a layer ofthe RMLC 320 shifts with respect to a deformation associated with thephase defect region in a previously deposited layer of the RMLC 320.

The laterally displaced phase defect region of the RMLC 320, similar tothe phase defect region of the RMLC 120 illustrated in FIG. 1, alters aphase of light reflected from the RMLC 320. However, when compared tothe phase defect region of the RMLC 120, the laterally displaced phasedefect region significantly reduces the accumulated phase shift errorand thus reduces its impact on the light reflected from the RMLC 320.More specifically, though each deformation in the layers 322 ₁, 322 ₂,322 ₃, 322 ₄, . . . 322 _(N) of the RMLC 320 causes a phase shift(error) in light reflected therefrom, because the deformations in thelayers 322 ₁, 322 ₂, 322 ₃, 322 ₄, . . . 322 _(N) are laterallydisplaced from one another (in other words, the lateral location of eachdeformation is different), light incident on the RMLC 320 sees fewerdeformations, resulting in fewer phase shifts (errors) in the lightreflected from the RMLC 320. In an example, the collective phase shifterror can result in constructive interference from the RMLC 320. Thelaterally displaced phase defect region of the RMLC 320 can thus enhanceimaging in lithography processes using the mask 300, even though themask 300 includes the defect 330 and associated laterally displacedphase defect region. It has also been observed that a laterallydisplaced phase defect region in a reflective multilayer coating, suchas the laterally displaced defect region of RMLC 320, associated withbump defects at the surface of a substrate, pit defects at the surfaceof the substrate, other defects at the surface of the substrate, ordefects in the reflective multilayer coating reduces printability ofsuch defects or phase defect regions, which can reduce line edgeroughness contributed by such defects or phase defect regions. Anallowable size of a defect or phase defect region in a mask may thus beincreased since the negative impact on the lithography process resultingfrom such defect or phase defect region is reduced by the lateraldisplacement characteristic, which increases a yield of mask blanks inmask manufacturing. Different embodiments may have different advantages,and no advantages are necessarily required of any embodiment.

The present disclosure provides for many different embodiments. Anexemplary method includes forming a reflective multilayer coating over asubstrate by tilting the substrate such that an angle α is formedbetween a normal line of the substrate and a landing direction ofparticles on the substrate and rotating the substrate about an axis thatis parallel with the landing direction of the particles. The angle α mayremain fixed during the forming of the reflective multilayer coating. Inan example, the angle α is greater than about 20 degrees and less thanabout 70 degrees. In an example, the forming the reflective multilayercoating includes depositing a plurality of layers over the substrate,such that the reflective multilayer coating includes a first layer and asecond layer deposited over the first layer; and the substrate is tiltedand rotated during the forming of the reflective multilayer coating suchthat a lateral location of a deformation in the second layer of thereflective multilayer coating is displaced by a distance from a laterallocation of a deformation in the first layer of the reflectivemultilayer coating. In an example, a defect is located at a surface ofthe substrate over which the reflective multilayer coating is formed;and the substrate is tilted and rotated during the forming of thereflective multilayer coating such that an amount of particles landingon a first side of the defect is different than an amount of particleslanding on a second side of the defect. In an example, the substrate istilted and rotated during the forming of the reflective multilayercoating such that a lateral location of a deformation associated withthe defect in a topmost layer of the reflective multilayer coating isdisplaced by a distance from a lateral location of the defect located atthe surface of the substrate. In another example, the reflectivemultilayer coating includes a defect, a first layer, and a second layerdeposited over the first layer; and the substrate is tilted and rotatedduring the forming of the reflective multilayer coating such that alateral location of a deformation associated with the defect in thesecond layer of the reflective multilayer coating is displaced by adistance from a lateral location of a deformation associated with thedefect in the first layer of the reflective multilayer coating.

An exemplary method for fabricating a mask includes depositing areflective multilayer coating over a substrate such that a laterallocation of a deformation in a subsequently deposited layer of thereflective multilayer coating is displaced by a distance from a laterallocation of a deformation in a previously deposited layer of thereflective multilayer coating, the subsequently deposited layer beingdeposited above the previously deposited layer. The depositing thereflective multilayer coating over the substrate includes tilting androtating the substrate to achieve the displaced lateral location of thedeformation in the subsequently deposited layer of the reflectivemultilayer coating. In an example, the substrate is rotated about anaxis that is parallel with a landing direction of deposited particles,and tilted such that an angle α is formed between a normal line of thesubstrate and a landing direction of deposited particles. An ion beamsputtering process may be used to deposit the reflective multilayercoating. In an example, depositing the reflective multilayer coatingincludes depositing a plurality of layer pairs, where each layer pairincludes a molybdenum layer and a silicon layer.

An exemplary mask includes a substrate; and a reflective multilayercoating deposited over the substrate, the reflective multilayer coatinghaving a first layer and a second layer deposited over the first layer.Due to the presence of a defect, the reflective multilayer coating has aphase defect region that includes a first deformation in the first layerat a first location, and a second deformation in the second layer at asecond location, the second location being laterally displaced from thefirst location. The second location is also vertically displaced fromthe first location. In an example, the phase defect region correspondswith a substrate defect located at a surface of the substrate; thereflective multilayer coating is deposited over the surface of thesubstrate; and the first location of the first deformation in the firstlayer is laterally displaced from a location of the substrate defect bya first distance and the second location of the second deformation inthe second layer is laterally displaced from the location of thesubstrate defect by a second distance. The second distance is greaterthan the first distance. The first location may be referred to as afirst lateral location (such as an x-coordinate of the first location),and the second location may be referred to as a second lateral location(such as an x-coordinate of the second location). The first layer may bea bottommost layer of the reflective multilayer coating, and the secondlayer may be a topmost layer of the reflective multilayer coating.Additional layers may be between the first layer and the second layer,where each of the additional layers includes a deformation and alocation of the deformation shifts laterally in successive additionallayer between the first layer and the second layer. In an example, thesubstrate is a low thermal expansion material (LTEM) substrate, and thereflective multilayer coating includes multiple layer pairs, such assilicon-molybdenum (Si—Mo) layer pairs. In an example, the firstdeformation in the first layer includes a first portion of the firstlayer having a first thickness and a second portion of the first layerhaving a second thickness, the first thickness being less than thesecond thickness; and the second deformation in the second layerincludes a first portion of the second layer having a third thicknessand a second portion of the second layer having a fourth thickness, thethird thickness being less than the fourth thickness. In an example, thereflective multilayer coating includes additional layers depositedbetween the first layer and the second layer, where each of theadditional layers includes a deformation. A lateral location of thedeformation in each additional layer is displaced in a same directionwith respect to a lateral location of a deformation of a previouslydeposited additional layer.

An exemplary lithography process may use the mask described herein. Forexample, the lithography process includes providing a mask having apattern, wherein the mask includes a substrate, and a reflectivemultilayer coating deposited over the substrate, the reflectivemultilayer coating having a first layer and a second layer depositedover the first layer. The reflective multilayer coating has a phasedefect region that includes a first deformation in the first layer at afirst location, and a second deformation in the second layer at a secondlocation, the second location being displaced laterally from the firstlocation. The lithography process further includes projecting radiationonto the mask such that the mask transfers a portion of the radiation toa wafer, thereby transferring the pattern of the mask to the wafer. Inan example, the radiation is extreme ultraviolet (EUV) radiation.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a reflectivemultilayer coating over a substrate, wherein the forming the reflectivemultilayer coating includes: tilting the substrate such that an angle αis formed between a normal line of the substrate and a landing directionof particles on the substrate; and rotating the substrate about an axisthat is parallel with the landing direction of the particles.
 2. Themethod of claim 1 wherein the angle α remains fixed during the formingof the reflective multilayer coating.
 3. The method of claim 1 wherein:the forming the reflective multilayer coating includes depositing aplurality of layers over the substrate, such that the reflectivemultilayer coating includes a first layer and a second layer depositedover the first layer; and the substrate is tilted and rotated during theforming of the reflective multilayer coating such that a laterallocation of a deformation in the second layer of the reflectivemultilayer coating is displaced by a distance from a lateral location ofa deformation in the first layer of the reflective multilayer coating.4. The method of claim 3 wherein a lateral displacement between thedeformation in the first layer and the deformation in the second layeris about 0.5 times to about 2.5 times a vertical displacement betweenthe deformation in the first layer and the deformation in the secondlayer.
 5. The method of claim 1 wherein: a defect is located at asurface of the substrate over which the reflective multilayer coating isformed; and the substrate is tilted and rotated during the forming ofthe reflective multilayer coating such that an amount of particleslanding on a first side of the defect is different than an amount ofparticles landing on a second side of the defect.
 6. The method of claim5 wherein the substrate is tilted and rotated during the forming of thereflective multilayer coating such that a lateral location of adeformation associated with the defect in a topmost layer of thereflective multilayer coating is displaced by a distance from a laterallocation of the defect located at the surface of the substrate.
 7. Themethod of claim 1 wherein: the reflective multilayer coating includes adefect, a first layer, and a second layer deposited over the firstlayer; and the substrate is tilted and rotated during the forming of thereflective multilayer coating such that a lateral location of adeformation associated with the defect in the second layer of thereflective multilayer coating is displaced by a distance from a laterallocation of a deformation associated with the defect in the first layerof the reflective multilayer coating.
 8. A method for fabricating amask, the method comprising: depositing a reflective multilayer coatingover a substrate such that a lateral location of a deformation in asubsequently deposited layer of the reflective multilayer coating isdisplaced by a distance from a lateral location of a deformation in apreviously deposited layer of the reflective multilayer coating, thesubsequently deposited layer being deposited above the previouslydeposited layer, and the deformations being associated with a samedefect.
 9. The method of claim 8 wherein the depositing the reflectivemultilayer coating over the substrate includes tilting and rotating thesubstrate to achieve the displaced lateral location of the deformationin the subsequently deposited layer of the reflective multilayercoating.
 10. The method of claim 9 wherein the rotating the substrateincludes rotating the substrate about an axis that is parallel with alanding direction of deposited particles.
 11. The method of claim 9wherein the tilting the substrate includes orienting the substrate suchthat an angle α is formed between a normal line of the substrate and alanding direction of deposited particles.
 12. The method of claim 8wherein the depositing the reflective multilayer coating over thesubstrate includes performing an ion beam sputtering process.
 13. A maskcomprising: a substrate; and a reflective multilayer coating depositedover the substrate, the reflective multilayer coating having a firstlayer and a second layer deposited over the first layer, wherein thereflective multilayer coating has a phase defect region that includes: afirst deformation in the first layer at a first location, and a seconddeformation in the second layer at a second location, wherein there islateral displacement between the second location and the first location.14. The mask of claim 13 wherein: the first deformation in the firstlayer includes a first portion of the first layer having a firstthickness and a second portion of the first layer having a secondthickness, the first thickness being less than the second thickness; andthe second deformation in the second layer includes a first portion ofthe second layer having a third thickness and a second portion of thesecond layer having a fourth thickness, the third thickness being lessthan the fourth thickness.
 15. The mask of claim 13 wherein: the firstlocation includes a first lateral location and a first vertical locationof a center of a full width at half maximum of the first deformation inthe first layer; the second location includes a second lateral locationand a second vertical location of a center of a full width at halfmaximum of the second deformation in the second layer; and the firstlateral location is different than the second lateral location and thefirst vertical location is different than the second vertical location.16. The mask of claim 15 wherein: a vertical distance, d_(y), is betweenthe first vertical location and the second vertical location; and alateral distance, d_(x), between the first lateral location and thesecond lateral location ranges from about 0.5 times to about 2.5 timesthe vertical distance (2.5 d_(y)≧d_(x)≧0.5 d_(y)).
 17. The mask of claim13 wherein: the phase defect region corresponds with a substrate defectlocated at a surface of the substrate; the reflective multilayer coatingis deposited over the surface of the substrate; and wherein the firstlocation of the first deformation in the first layer is laterallydisplaced from a location of the substrate defect by a first distanceand the second location of the second deformation in the second layer islaterally displaced from the location of the substrate defect by asecond distance, the second distance being greater than the firstdistance.
 18. The mask of claim 13 wherein the first layer is abottommost layer of the reflective multilayer coating and the secondlayer is a topmost layer of the reflective multilayer coating.
 19. Themask of claim 18 wherein the reflective multilayer coating includesadditional layers deposited between the first layer and the secondlayer, wherein each of the additional layers includes a deformation, andfurther wherein a lateral location of the deformation in each additionallayer is displaced in a same direction with respect to a laterallocation of the deformation of a previously deposited additional layer.20. A lithography method comprising: providing a mask having a pattern,wherein the mask includes: a substrate having a feature, and areflective multilayer coating deposited over the substrate, thereflective multilayer coating having a first layer and a second layerdeposited over the first layer, wherein the reflective multilayercoating has a phase defect region that includes: a first deformation inthe first layer at a first location, the first deformation based on thefeature, and a second deformation in the second layer at a secondlocation, the second deformation based on the feature, wherein there islateral displacement between the second location and the first location,wherein the second deformation is laterally displaced within thereflective multilayer coating such that the second deformation does notoverlap the feature; and projecting radiation onto the mask such thatthe mask transfers a portion of the radiation to a wafer, therebytransferring the pattern of the mask to the wafer.